Veneer sheet separator

ABSTRACT

Conveyors feed veneer sheets to a plywood assembly station in sequence for assembly. Sometimes two veneer sheets, one superposed upon another, are fed on one conveyor. Such a condition is automatically remedied by a veneer sheet separator formed by the conveyor and appurtenant equipment. The condition is detected automatically by sensing means which activate control means that are subsequently operated by a veneer sheet reaching a position on the conveyor and when operated actuate a vacuum head. One veneer sheet is gripped by the vacuum head while the other veneer sheet is forced downstream by the conveyor causing separation by shearing action between the veneer sheets.

United States Patent 2,813,717 11/1957 Mentzer Inventor Terence H. West San Jose, Calif. Appl. No. 887,877 Filed' Dec. 24, 1969 Patented Aug. 17, 1971 Assignee FMC Corporation San Jose, Calif.

VENEER SHEET SEPARATOR 7 Claims, 14 Drawing Figs. U.S. Cl 271/14, 214/85 D, 271/26, 271/47, 271/57 Int. Cl B65h 5/10 Field ofSearch 271/10,11, 12,13,14, 47, 57, 26,56, 54;2l4/8.5 D; 270/56 References Cited UNITED STATES PATENTS 3,258,262 6/1966 Rehm 3,501,138 3/1970 McGeeetal.

27l/56X 271/26X ABSTRACT: Conveyors feed veneer sheets to a plywood assembly station in sequence for assembly. Sometimes two veneer sheets, one superposed upon another, are fed on one conveyor. Such a condition is automatically remedied by a veneer sheet separator formed by the conveyor and appurtenant equipment. The condition is detected automatically by sensing means which activate control means that are subsequently operated by a veneer sheet reaching a position on the conveyor and when operated actuate a vacuum head. One veneer sheet is gripped by the vacuum head while the other veneer sheet is forced downstream by the conveyor causing separation by shearing action between the veneer sheets.

PATENTED AUG! 7 19?:

SHEEI 1 0F 5 INVENTOR TERENCE H. WEST VENEER SHEET SEPARATOR CROSS-REFERENCE TO RELATED APPLICATIONS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to sheet feeding or delivering'by separators and conveyors, and more particularly, to a conveyor with apparatus for automatically separating a plurality of veneer sheets, one superposed upon another, and thereby delivering single sheets in sequence.

2. Description of the Prior Art Veneer sheet conveyors are used in plywood layup apparatus for feeding veneer to a plywood assembly station. Different grades of veneer are sometimes used for face, middle and back panels with glued core strips interspersed between to form five-ply plywood. Plywood is assembled manually in sandwich fashion at the assembly station by operators who place veneer sheets and glued core strips together in sequence. Such apparatus is disclosed in the pending application of Ronald J. Billett et al., U.S. Ser. No. 811,929, which has been assigned to the same assignee as this application.

Veneer sheets sometimes stick together when they are lifted from a stack and fed to a conveyor. A problem is encountered when a plurality of veneer sheets, one superposed upon another, are fed on the conveyor to the assembly station. In such case, there is an extra sheet that must be discarded by the operators because the assembly feeding sequence continues selectively on the basis of a single sheet feed. While the previously mentioned pending patent application shows means for detecting and warning operators of doubles on the conveyor, it is necessary for the operators to manually remove and discard the extra veneer sheet.

SUMMARY OF THE INVENTION The present invention provides for automatically detecting and separating double veneer sheets to regulate the conveyor discharge to single veneer sheets in sequence. Plywood assembly operators are thereby fed veneer sheets in effective order for assembly and are not distracted by having to separate doubles. Thus, the plywood assembly operation is more efficient and enables increased production together with a savings in cost.

To eliminate doubles, sensing means detect when a plurality of veneer sheets, one superposed upon another, are on the conveyor and activate control means which actuate a vacuum head to grip one veneer sheet, while the other veneer sheet is moved therefrom by the conveyor. Thus, one veneer sheet is separated from the other by shearing action.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic diagram showing the conveyor drives and illustrating certain operational steps of the present invention.

FIG. 2 is a schematic diagram showing framework and the location of limit switches for controlling the apparatus of the present invention.

FIG. 3 is an enlarged partial side view, partly in cross section, ofa veneer storage station.

FIG. 4 is an enlarged fragmentary side view, with parts broken away for clarity, of a movable gate which controls movement of veneer sheets on a conveyor.

FIG. 5 is an enlarged fragmentary side view showing a typical frame mounting of bearing blocks for nip rollers which urge the veneer toward the assembly station.

FIG. 6 is a section taken on the line 6-6 of FIG. 3.

FIG. 7 is an enlarged schematic diagram of a valve which regulates the stationary vacuum head.

FIG. 8 is a schematic diagram of a pneumatic circuit which regulates operation of a movable gate, like shown in FIG. 4, and a movable vacuum head.

FIG. 9 is a schematic diagram of the electrical circuit for the apparatus of the present invention.

FIGS. 10-14 are schematic views illustrating sequential operations of the plywood layup apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENT Looking now at FIGS. 1 and 2, plywood layup apparatus 14 feeds veneer sheets from a plurality of storage stations to a plywood assembly station 15. Back veneer sheets in stack 16a are supported on an elevator or lift table 18 at a rear storage station. Middle veneer sheets in stack 16b are supported on lift table 20 at a front storage station and face veneer sheets in stack 16c are supported on lift table 19 at a middle storage station. An upper conveyor 21 feeds back veneer sheets from stack 16a to an upper ready station conveyor 22 and an intermediate conveyor 23, positioned vertically beneath the upper conveyor 21, feeds face veneer sheets from stack to the upper ready station conveyor, also. Middle veneer sheets are fed from stack 16b at the front storage station directly onto a lower ready station conveyor 24. Back and face veneer sheets are released together by the upper ready station conveyor to assembly station 15 and middle veneer sheets are released alternately from the lower ready station conveyor to the assembly station. Core strips, not shown, are supplied to the assembly station from another direction after passing through a gluing machine, also not shown.

The plywood assembly apparatus 14 includes a frame 25, shown in FIG. 2, that provides horizontal and vertical support for conveyors 21, 22, 23 and 24. Furthermore, the frame supports a carriage 26 at each storage station for feeding veneer sheets from a respective lift table to a respective conveyor.

Lift tables l8, l9 and 20 are of the type disclosed in U.S. Pat. No. 3,110,476 of WA. Farris which issued Nov. 12, 1963. These lift tables automatically elevate a stack of veneer sheets to a level that enables a carriage 26 at each storage station to feed one veneer sheet at a time to a respective conveyor. Lift table hydraulic and electric control circuits are shown in the previously mentioned patent application of Ronald J. Billett et al., U.S. Ser. No. 811,929 and are incorporatedherein by reference.

With reference to FIG. 6, at each storage station, a rail R is mounted on one side of the frame 25 and a rail R is mounted on the opposite side of the frame. These rails form a track upon which carriage 26 travels. This carriage is formed by a hollow duct 27 that extends transversely of the rails with one end of the duct slidably connected to rail R by a bracket 28 and a beam 29 mounted intermediately on the duct is fixed to arm 30 that slidably rides on rail R A fan housing 31 containing a fan, not shown, is mounted at the end of the hollow duct extending outward from rail R and a motor 4MTR is mounted on the fan housing to drive the fan. A skirt 32 is mounted on the hollow duct surrounding a bottom opening located intermediately between the rails and when the fan motor is energized to drive the fan, air is evacuated from the hollow duct creating a vacuum at the bottom opening within the skirt.

Carriage 26 is advanced and retracted by a pneumatic actuator 33 having a cylinder 34 connected to frame 25. As shown in FIG. 8, the cylinder has a piston 35 therein which is connected by a connecting rod 36 and a link 37 to beam 29. Pneumatic lines 38 and 39 are connected to opposite ends of the cylinder in order to introduce air pressure on either side of the piston. A control valve 40 has a movable stem 41 therein to control airflow from pressure line 42 to lines 38 and 39. This valve is controlled by a solenoid 4 SOL and when deenergized, the movable stem is in the position shown. Line 39 is pressurized causing piston 35 to retract, while line 38 is vented to atmosphere throughthe valve discharge line 43 which contains a restriction 43R for adjusting retraction of the piston. When the solenoid is energized, the movable valve stem is shifted to the right to allow pressure to flow through the valve from line 42 to line 38 and line 39 is vented to atmosphere through discharge line 44 which contains a regulating restriction 44R. Thus, pressure is introduced behind piston 35 causing it to advance or move forward.

During feeding operation, motor 4MTR drives the fan continuously so that there is always a vacuum pressure at the opening within skirt 32. Lift tables 18, 19 and 20 maintain veneer sheets in a position for the uppermost sheet to be gripping by suction force due to the vacuum within the skirt. Carriage 26 then moves forward when solenoid 4 SOL is energized to feed the veneer sheet to a respective conveyor 21, 23 or 24. A funnel guide 46, shown in FIG. 3, is positioned at the downstream side of each storage station and has converging panels forming top, bottom, and sides to guide a veneer sheet between a pair of nip or pinch rollers 47 and 48 which strip the veneer sheet from the skirt.

On each pair of nip or pinch rollers, the upper roller 48 is journaled at each end in an upper bearing block 49 (see FIG. 5) mounted on studs 50 that are received in a bracket 41 secured to frame 25. The studs are threadably fitted through the bracket and extend through lower bearing block 52 which is secured in place by nuts 53 that fit on the studs. Springs 54 are mounted on the studs between head portions thereof and the upper bearing block to urge the upper bearing block downward towards the bracket. Each time a sheet of veneer passes between the nip rollers, the upper nip roller and bearing blocks yield, compressing the springs. Thus, the upper nip roller is resiliently urged towards the lower nip roller forcing the veneer sheet into driving contact with the lower nip roller to separate the veneer sheet from skirt 32.

Sometimes, two veneer sheets will stick together and both will be fed between upper nip roller 48 and lower nip roller 47 as illustrated in FIG. 1 at the rear storage station, In such event, the upper nip roller together with bearing blocks at each end thereof will be elevated sufficiently to operate limit switches 23LS and 24LS mounted over the upper left and right bearing blocks, respectively. It is desirable to have limit switches over each upper bearing block, at both sides of the upper nip roll, because sometimes surface irregularities on a veneer sheet will cause one bearing block to rise but normally only two veneer sheets will operate both limit switches. Thus, the nip rollers and limit switches at each conveyor are means which sense when a plurality of veneer sheets, one superposed upon another, are fed on the conveyor.

As best shown in FIGS. 1 and 3, veneer sheets are fed from the rear and middle storage stations to upper ready station conveyor 22 by upper conveyor 21 and intermediate conveyor 23, respectively. These conveyors are positioned in closely tacked relationship and are formed by rollers 55 driven by an endless belt 56 trained about a pair of pulleys 57. On each of the conveyors, the rollers are turned slightly to one side to guide veneer against a sideplate for alignment.

Upper conveyor 21 is driven by a motor SMTR connected by chain 58 to a sprocket 59 that drives pulley 57 at the upstream end of the conveyor. Since the upper conveyor has two endless belts 56, drive is transmitted from the upstream belt to the downstream belt through a chain 60 trained about sprockets 61 and 62 at the inner ends of adjoining pulleys 57. Power is transmitted from sprocket 59 by chain 63 to a sprocket 64 which turns the lower nip roller 47. The upper nip roller 48 is normally engaged with the lower nip roller and rotates therewith or rotates on the surface of a veneer sheet passing between the nip rollers, A chain 65 transmits power to a sprocket 66 that drives a brush 67 for sweeping veneer as it emerges from the nip rollers. A similar drive system is provided for intermediate conveyor 23 and upper ready station conveyor 22 so like numbers are used to identify like parts with the exception that the motor is identified as 7MTR.

The drive system for lower ready station conveyor 24 has a motor 9MTR which drives a chain 68 that turns a sprocket 69 connected to pulley 57 at the upstream end of the conveyor, A chain 70 engaged by sprocket 69 drives lower nip roller 47 through sprocket 71 mounted on the roller, which in turn drives the upper nip roller 48. A chain 72 transmits power from sprocket 71 to a sprocket 73 on a brush 74. From sprocket 73, power is transmitted by chains and 76, connected in driving relation through a double idler sprocket unit 77, to a drive sprocket 78 on a lower nip roller 47, above the upper ready station conveyor 22. Upper nip roller 48 thereof is driven by lower nip roller 47.

With reference to FIG. 1, upper conveyor 21 has a gate G-l located midway between upstream and downstream endless belts 56 and a gate G-2 at the downstream end thereof. Intermediate conveyor 23 has a gate G-3 located at the downstream end thereof before the upstream end of upper ready station conveyor 22. A gate 0-4 is located at the downstream end of upper ready station conveyor 22 and a gate G-5 is located at the downstream end of lower ready station conveyor 24. Each gate extends between side members of the plywood layup apparatus frame 25 (FIG. 2) and is pivotably mounted to move between an upright blocking position, as shown in solid line (FIG. 4), and a lowered nonblocking position, as indicated in phantom line. Gate G-3, shown in FIG. 4, is typical of each gate and pivots about axis 68 in response to movement of an arm 69 attached thereto. A pneumatic actuator 70 attached to frame 25 has a piston rod 71 connected to the arm for moving the gate.

Pneumatic actuator 70 has a cylinder 73, shown in FIG. 8, with a piston 74 slidably received therein and connected to one end of the piston rod 71. An air line 75 is connected to the cylinder behind the piston and an air line 76 is connected to the cylinder in front of the piston. A valve 77 is coupled to air lines 75 and 76 and to pressure line 42 which is supplied by a source of compressed air. Air movable spool 78 slidably fitted within the valve is operated by a solenoid 7SOL to control operation of the pneumatic actuator. When the solenoid is deenergized, the movable spool is in the position shown and compressed air from line 42 passes through the valve into line 75 and behind piston 74. Thus, piston rod 71 is extended and gate G-3 positioned upright to block veneer. The cylinder in front of the piston is vented to atmosphere through line 76, valve 77 and a discharge line 79 which has a control restriction 79R therein. When solenoid 7SOL is energized, spool 78 moves to the left of the position shown to direct air pressure from line 42 through the valve into line 76 and in front of the piston. Air behind the piston escapes through line 75, valve 77 and a discharge line 80 which has a control restriction 80R therein to limit the rate of retraction of the piston. With piston rod 71 retracted, gate 0-3 is pivoted to a horizontal position that enables veneer to pass.

Looking now at FIGS. 1 and 2, a sheet sensor switch llLS is located upstream of gate 6-] and spaced downstream from nip rollers 47 and 48 of upper conveyor 21 by a distance that exceeds the length of a sheet of veneer. This sheet sensor switch is operated by contact with a sheet of veneer at gate G-l. Similarly, sheet sensor switch 17LS is operated by a veneer sheet at gate G2; sheet sensor switch 13LS is operated by a veneer sheet at gage G-3; sheet sensor switch 20LS is operated by a veneer sheet at gate G-4; and sheet sensor switch 41LS is operated by a veneer sheet at gate G-5. These sheet sensor switches are means for controlling operation of the gripping means which will now be described.

A stationary vacuum head is located downstream from nip rollers 47 and 48 above upper conveyor 21, as shown in FIG. 1, and constitutes means for gripping a veneer sheet. The vacuum head is spaced upstream from gate G-l by a shorter distance that the length of a veneer sheet and when a pair of veneer sheets, one superposed upon another, are retained by gate 0-1, the vacuum head can be activated to grip by suction the upstream end of the upper veneer sheet. As shown in FIGS. 3 and 6, a pair of angles 86 and 87 extend transversely of frame 25 above upper conveyor 21 and vacuum head 85 is suspended from these angles. A solenoid valve 88. shown in FIG. 7, is positioned between vacuum head 85 and line 89, which is connected to a vacuum source, not shown. When solenoid 8SOL is deenergized, a valve core 90 within valve 88 vents the vacuum head to atmosphere but when the solenoid is energized, the valve core is moved to the right sealing the vent and providing flow communication between the vacuum head and source line. Thus, the vacuum head is evacuated and suction within the head causes the upper veneer sheet to be gripped.

.A vacuum head 92 is located above intermediate conveyor 23 and a vacuum head 93 is located above lower ready station conveyor 24. These vacuum heads are similar to vacuum head 85 and no further description is believed necessary.

Complete electrical control circuits for plywood layup apparatus of the type shown have been disclosed in the previously mentioned patent application of Ronald J. Billett et al., U.S. Ser. No. 81 L929. The electrical circuit shown in FIG. 9 represents the controls for stationary vacuum head 92 and it will be understood that similar circuits are provided for vacuum heads 85 and 93. a v

Limit switches 23LS and 24LS close when two veneer sheets are positioned between nip rollers 47 and 48 of intermediate conveyor 23, as shown in FIG. 10. Stepping switch 2SSW is .thereby energized and cocked. When the veneer sheets pass through the nip rolls, as shown in FIG. 11, the limit switches open, deenergizing the stepping switch, which thereupon steps to close contacts 2SSW-l and 2SSW-2. When the two veneer sheets contact sheet sensor switch 13LS, as shown in FIG. 12, normally closed contact 13LS-I opens and normally open contacts 13LS-2 and l3LS-3 close. The opening of contacts I3LS-1 deenergized solenoid 4SOL and carriage 26 returns to a retracted position. Nothing happens with the closing of contacts 13LS-2 but when contacts 'l3LS-3 close, solenoid 8SOL is energized along with air horn AH which sounds. Suction is provided at vacuum head 92 when solenoid 8SOL is energized and the upper veneer sheet is gripped, as shown in FIG. 12.

Both veneer sheets will be retained behind gate G-3 as long as there is a veneer sheet on the upper ready station conveyor 22 holding limit switch LS open. When the veneer passes, as shown in FIG. 13, limit switch 20LS closes and solenoid 7SOL is energized to open gate G-3. Relay ISCR is also energized to close contacts l8CR-l and thereby energize stepping switch 2SSW for cocking action. The lower veneer sheet is conveyed downstream over gate G-3 onto the upper ready station conveyor 22, as shown in FIG. 13, while the upper veneer sheet is retained by vacuum head 92. The upper veneer sheet holds limit switch 13LS open but when the lower veneer sheet opens limit switch 20LS, as shown in FIG. 14, relay 18CR is deenergized and contact 18CR-1 opens. Thus, stepping switch 2SSW is deenergized and steps to open contact 2SSW1 and contact 2SSW-2. Solenoid 8SOL is deenergized along with the air horn AH and upper veneer sheet is released by the vacuum head 92, as shown in FIG. 14. The two veneer sheets are now separated and spaced so that normal operation follows.

From the foregoing description, it will be seen that upper conveyor 21, intermediate conveyor 23 and lower ready station conveyor 24, together with appurtenant equipment, each constitute a veneer sheet separator. Operation of intermediate conveyor 23 for the separation of "doubles is typical and has been described with reference to the electrical circuit shown in FIG. 9.

Although the best mode contemplated for carrying out the present invention has been herein shown and described, it will be apparent that modification and variation may be made without departing from what is regarded to be the subject matter of the invention.

What I claim is:

1. Apparatus for laying up single sheets of plywood veneer or the like from a stack of sheets, said apparatus comprising a sheet conveyor; means for normally feeding the upper sheet of the stack to said conveyor; means for sensing when a plurality of veneer sheets, one super osed upon another, are being fed onto the conveyor; means or arresting the feed of the uppermost veneer sheet; and means for causing said arresting means to arrest the feed of the upper sheet in response to the sensing of a plurality of veneer sheets by said sheet-sending means; said conveyor thereafter continuing to feed the lowermost of said plurality of sheets.

2. The apparatus described in claim 1 wherein said sheetfeed-arresting means includes a vacuum head adapted to grip and retain the uppermost veneer sheet which the lower veneer sheet is moved from thereunder by the conveyor.

3. The apparatus described in claim 2, including means for separating the uppermost veneer sheet from the vacuum head after the lower veneer sheet has been spaced therefrom.

4. The apparatus described in claim 2 wherein said sensing means includes a pair of nip rollers located at the upstream end of the conveyor, said vacuum head is located in a stationary position spaced above the conveyor and downstream from the nip rollers, and said means for causing said arresting means to arrest the feed of the upper veneer sheet includes a sheet sensor switch located downstream from the vacuum head by a distance that enables the upstream ends of a plurality of veneer sheets to clear the nip rollers before the vacuum head is activated.

5. The apparatus described in claim 3 wherein the veneersheet-separating means includes a valve to shut off the vacuum source from the vacuum head.

6. The apparatus described in claim 4 wherein the vacuum head is spaced above the conveyor by a height sufficient to enable a pair of veneer sheets in superposed relationship to pass thereunder but close enough that when suction is applied to the vacuum head, the veneer sheet adjacent the vacuum head will be gripped thereby.

7. In plywood layup apparatus, a veneer sheet separator comprising: a power-driven roller conveyor for moving veneer sheets between a storage station and an assembly station; a pair of pinch rollers located at the upstream end of the roller conveyor to transfer veneer sheets to the conveyor; means responsive to displacement of one pinch roller to detect the presence of more than one sheet of veneer between the pinch rollers; a vacuum head located adjacent the conveyor to grip the upper veneer sheet while the lower veneer sheet is driven downstream by the conveyor; a sheet sensor switch that detects the presence of veneer sheets downstream from the vacuum head after more than one veneer sheet has been detected passing through the pinch rollers; and a gate located downstream of the conveyor from the sheet sensor switch to control the flow of veneer sheets on the conveyor and to stop veneer sheets with their upstream ends located adjacent the vacuum head; said gate being operated in response to demand for veneer sheets, opening to permit the lower veneer sheet to pass downstream while the upper veneer sheet is retained by the vacuum head and closing after the lower veneer sheet passes to retain the upper veneer sheet which is released by the vacuum head upon closing of the gate.

FWD) UNITED STATES PATENT OFFICE (5/69) CERTIFICATE OF CORRECTION Patent No. ,969 Dated August 17, 1971 TERRENCE H. WEST Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 3, line 22, after "bracket" change "41 to 51 Col. 4, line 60, before "G-3" change "gage" to gate Col. 4, line 75, after "solenoid" insert operated Col. 5, line 31, change "deenergized" to deenergizes Sirzned and sealed this Lrth day of July 1972.

(SEAL) Attest:

EDWARD M.I"LETCHER,JR. ROBERT GOTTSGHALK Attesting Officer Commissioner of Patents 

1. Apparatus for laying up single sheets of plywood veneer or the like from a stack of sheets, said apparatus comprising a sheet conveyor; means for normally feeding the upper sheet of the stack to said conveyor; means for sensing when a plurality of veneer sheets, one superposed upon another, are being fed onto the conveyor; means for arresting the feed of the uppermost veneer sheet; and means for causing said arresting means to arrest the feed of the upper sheet in response to the sensing of a plurality of veneer sheets by said sheet-sending means; said conveyor thereafter continuing to feed the lowermost of said plurality of sheets.
 2. The apparatus described in claim 1 wherein said sheet-feed-arresting means includes a vacuum head adapted to grip and retain the uppermost veneer sheet which the lower veneer sheet is moved from thereunder by the conveyor.
 3. The apparatus described in claim 2, including means for separating the uppermost veneer sheet from the vacuum head after the lower veneer sheet has been spaced therefrom.
 4. The apparatus described in claim 2 wherein said sensing means includes a pair of nip rollers located at the upstream end of the conveyor, said vacuum head is located in a stationary position spaced above the conveyor and downstream from the nip rollers, and said means for causing said arresting means to arrest the feed of the upper veneer sheet includes a sheet sensor switch located downstream from the vacuum head by a distance that enables the upstream ends of a plurality of veneer sheets to clear the nip rollers before the vacuum head is activated.
 5. The apparatus described in claim 3 wherein the veneer-sheet-separating means includes a valve to shut off the vacuum source from the vacuum head.
 6. The apparatus described in claim 4 wherein the vacuum head is spaced above the conveyor by a height sufficient to enable a pair of veneer sheets in superposed relationship to pass thereunder but close enough that when suction is applied to the vacuum head, the veneer sheet adjacent the vacuum head will be gripped thereby.
 7. In plywood layup apparatus, a veneer sheet separator comprising: a power-driven rollEr conveyor for moving veneer sheets between a storage station and an assembly station; a pair of pinch rollers located at the upstream end of the roller conveyor to transfer veneer sheets to the conveyor; means responsive to displacement of one pinch roller to detect the presence of more than one sheet of veneer between the pinch rollers; a vacuum head located adjacent the conveyor to grip the upper veneer sheet while the lower veneer sheet is driven downstream by the conveyor; a sheet sensor switch that detects the presence of veneer sheets downstream from the vacuum head after more than one veneer sheet has been detected passing through the pinch rollers; and a gate located downstream of the conveyor from the sheet sensor switch to control the flow of veneer sheets on the conveyor and to stop veneer sheets with their upstream ends located adjacent the vacuum head; said gate being operated in response to demand for veneer sheets, opening to permit the lower veneer sheet to pass downstream while the upper veneer sheet is retained by the vacuum head and closing after the lower veneer sheet passes to retain the upper veneer sheet which is released by the vacuum head upon closing of the gate. 